1. Field of the Invention
The present invention relates to a method of enhancing image display efficiency and a related apparatus, and more particularly to a method of enhancing image display efficiency and a related apparatus, using blank reducing.
2. Description of the Prior Art
According to vision persistence of human eyes' nature, an image-displaying manner for a cathode ray tube (CRT) display is developed to emit an electron beam scanning on the screen line-by-line rapidly to represent natural colors in electrical waveforms. An electron gun of the CRT emits the electron beam from one side of a horizontal line to the other side, and then moves to scan the next horizontal line from the same start side. The electron gun needs a positioning time to move and locate the start point of the next horizontal line and meanwhile no electron beam is emitted. Moreover, the CRT demands a signal to inform the electron gun to start to scan at certain time. According to a video timing specification provided for the CRT, a defined frame signal includes a horizontal component and a vertical component. The horizontal component includes image data with respect to each horizontal line and blank signals, each arranged between image data and image data. Each blank signal includes a front porch signal, a horizontal synchronization signal (Hsync) and a back porch signal. The front and back porch signals carry no information in order to provide the positioning time for the electron gun to move and locate the next horizontal line. The Hsync signal is utilized to inform the electron gun the time to start to scan. After a whole frame is scanned line by line, the electron tube moves back to the left-top corner of the screen and restarts a new frame scanning. As a result, the vertical component also provides a vertical front porch signal, a vertical synchronization signal (Vsync) and a vertical back porch signal and the functions thereof are the same as the corresponding signals of the horizontal component. A detailed specification is referred to Generalized Timing Formula (GTF) provided by the Video Electronics Standards Association (VESA).
With evolution of imaging technologies, LCDs have gradually replaced CRTS. A driving circuit of the LCD is used for driving the liquid crystals of the panel and includes gate drivers and source drivers. The gate drivers transmit scan signals to the scan lines (horizontal lines) so as to turn corresponding pixels on or off. The source drivers transmit image data signals to data lines so as to drive the liquid crystals. For a LCD, there are various functions available, such as resolution setting, display size change (ex. 4:3 or 16:9), and frame rate adjustment. Those functions involve image processes and timing technology. As a LCD of the prior art builds those functions, the performance may be restricted under the transmission bandwidth and buffer size. Take a LCD following the GTF for example. An internal buffer first duplicates the horizontal component of the frame signal. The original frame signal and its duplicated signal are performed required image processes and then displayed in a shorter period to increase the frame rate. However, as the frame rate is adjusted to a very high rate, the duplication for the frame signal may occupy large memory since the horizontal blank signals of the frame signal are duplicated with the image data. Therefore, large-space buffers are required for the LCD of the prior art to realize those functions.
Assume that a LCD of the prior art follows the VESA timing specification, and adopts a transmission interface with low voltage differential signaling (LVDS) technology having a maximum bandwidth of 85-90 MHz. The LCD displays video with a 1280×1024 resolution and a 60 Hz frame rate. In light of the VESA timing specification, horizontal and vertical pixels for each frame are 1688 and 1066 pixels, respectively. Normally the horizontal pixel number is 1.3 times the horizontal resolution while the vertical pixel number is 1.05 times the vertical resolution. The data rate can be calculated by the following formula:Data Rate=the horizontal pixel number×the vertical pixel number×the frame rate÷the channel number of the LVDS=1688×1066×60÷2=53.98 MHz
The calculation result shows that the data rate with respect to the 60 Hz frame rate is smaller than the maximum bandwidth. As the frame rate is adjusted to be 100 Hz, the data rate becomes 89.97 MHz, achieving the maximum bandwidth limit. As the frame rate is adjusted to be 120 Hz, the data rate is calculated as 107.96 MHz, exceeding the maximum bandwidth limit. The LVDS transmission interface cannot afford such high data rate. That is, the LCD is incapable of displaying video with a 120 Hz frame rate. The LCD eliminates the moving and positioning issues of the electron gun, but instead has to deal with switching delay and data transmission delay. The LCD requires much shorter preparation time than the CRT, and therefore the blank signal of the timing specification appears redundantly long when applied to the LCD, especially for the front and back porch signals. Therefore, as the LCD of the prior art adopts the traditional timing specification, various functions could be limited in their expansibility and flexibility.
Therefore, there is a high cost involved for the LCD of the prior art to go in quest of high bandwidth transmission interface and large-space buffer to achieve the functions in a wide practical range, such as frame rates available from 60 Hz to 120 Hz. The related LCD performance is restricted.